1. Field of the Invention
The invention relates to a printer having a USB interface and at least an interface other than the USB interface.
2. Related Background Art
The Universal Serial Bus (USB) interface which has formally been supported since Windows (registered trademark) 98 is a new interface which is substituted for conventional IEEE1284. The USB interface has the following features.                1) Devices having various functions can be connected.        
(IEEE1284 is originally an interface only for use for printers.)                2) “Plug & Play” is possible.        3) Up to 127 apparatuses can be connected via a hub.        
And the like.
To realize “Plug & Play”, in the USB, the device has a bus termination as shown in FIG. 3.
In FIG. 3, reference numeral 300 denotes a host side and 301 indicates a function. The termination on the host 300 side has been pulled down and one of signals on the function 301 side has been pulled up. In the case of the USB fast speed function, D+ has been pulled up. In the case of the USB slow speed function, D− has been pulled up. (Note: In the USB, there are two transfer speeds of 12 Mbits and 1.5 Mbits. The function for performing the 12-Mbit transfer is called a fast speed function and the function for performing the 1.5-Mbit transfer is called a slow speed function. In the USB, the host and hub have to be able to support both of the fast speed transfer and the slow speed transfer.) Therefore, if the host 300 and the function 301 are connected by a USB cable and a power source of the function 301 is turned on, since the signal D+ or D− is pulled up, one of the signal D+ and D− on the host side is set to the high level. The host 300 detects that D+ or D− of the USB data signal has been set to the high level, thereby recognizing that the USB function has physically been connected. When the host 300 confirms that the function 301 has been connected, the host issues a command to confirm what the connected function is. When the function 301 receives the command from the host 300, the function 301 returns information of a device class or a device model name or the information of the device class and the device model name to the host 300. For example, if the function 301 is a printer, the host recognizes that the function 301 belongs to the class of the printer from the received information of the device class or the received information of the device model name and issues a command of the printer class.
If the function 301 belongs to the class of a pointing device (human interface device), the host recognizes that the function 301 is the class of the pointing device (human interface device) from the received information of the device class or the received information of the device model name and issues a command of the class of the pointing device (human interface device).
Such a process for confirming what the connected function is is called enumeration.
Although the USB has formally been supported in Windows (registered trademark) 98, there are many apparatuses which support only conventional IEEE1284 such as personal computers before the release of Windows (registered trademark) 98, apparatuses other than the personal computers, and the like. Therefore, if the printer supports both of the USB and IEEE1284 until the USB is widely spread, it benefits the user. FIG. 4 shows a constructional diagram of a printer having both of the USB and IEEE1284. In FIG. 4, in the case of printing via IEEE1284, print data and a print command which are sent from an upper apparatus are stored from an IEEE1284 cable 115 into a buffer 113 via an IEEE1284 I/F 106, a USB/IEEE selector 107, and a buffer controller 108. A CPU 101 interprets and modifies the print command and print data stored in the buffer 113 and controls in accordance with the print command in a manner such that a motor controller 110 controls a CRMotor/LFMotor (not shown) via a motor driver 112 and a print head controller 109 controls a print head 111 to output the print data. While printing, the CPU is heavily loaded with interpretation and modification of the print command and print data sent from the upper apparatus, motor control, and print head control. When the USB cable is connected and the foregoing enumeration is started during the printing, the CPU is burdened with the enumeration, so that there is a possibility of occurrence of                1) decrease in printing speed        2) impossibility of enumeration        
Particularly, in the case of a printer of a low price, a cheap CPU whose processing ability is low is often used, so that such a possibility increases.